Strange Lava World Is Shriveled Remains of Former Self

The first rocky planet confirmed to be orbiting another star
is truly one strange world, with rock rains, potentially raging volcanoes, and huge
temperature differences between its night and day sides. This hellish rock
might also be the remnant core of a former gas giant whose atmosphere long ago
evaporated away.

CoRoT-7b (named after the French telescope that discovered
it) is a so-called "Super-Earth" orbiting a star about 480
light-years from Earth.

Weighing in at just five times the mass of Earth and not
quite two times the Earth's radius, this extrasolar
planet was the first of the more than 400 that have been
found to date that was confirmed to be a rocky
world, instead of a gas giant.

But this exoplanet is anything but Earth-like.

CoRoT-7b orbits just 1.6 million miles (2.5 million km) out
from its parent star, or 23 times closer than Mercury is to the sun in our
solar system. This close proximity sends temperatures on the star-facing side
of the planet up to a hellish 4,000 degrees Fahrenheit (2,200 degrees Celsius).

The planet is tidally-locked, so the same side is always
facing its star (just as the moon only presents one face to the Earth). The far
side of the planet is therefore always in shadow, and temperatures there dip
down as low as minus 350 F (minus 210 C).

The possibility that CoRoT-7b?s current appearance may just
be the shriveled remains of a former gas giant glory also casts another oddity
atop the pile.

"CoRoT-7b may be the first in a new class of planet -
evaporated remnant cores," said Brian Jackson of NASA's Goddard Space
Flight Center in Greenbelt, Md.

Rock rains and volcanoes

The temperatures on the star-facing side of the planet are
so hot that they can vaporize rock. Scientists who modeled the atmosphere of
CoRoT-7b determined that the planet likely has no volatile gases (carbon
dioxide, water vapor, nitrogen), and is instead likely made up of what could be
called vaporized rock.

The atmosphere of CoRoT-7b could have weather systems that
unlike the watery weather on Earth cause pebbles to condense out of the air and
rain
rocks onto the molten surface of the planet.

And if the planet doesn't already sound inhospitable to
potential alien life, it also could be a volcanic nightmare.

New evidence presented last week at the annual meeting of
the American Astronomical Society (AAS) in Washington, D.C., suggests that if
CoRoT-7b's orbit is not perfectly circular, gravitational tugs from one of its
two sister planets could push and pull the surface, creating friction that
heats the interior of the planet. This heating could cause extensive
volcanism across the planet's surface, with even more explosive activity
than Jupiter's moon Io, which has over 400 volcanoes.

If this turns out to be the case, as scientists' models
suggest, CoRoT-7b could be a new class of exoplanet, the Super-Ios, said one of
the researchers who made the finding, Rory Barnes of the University of
Washington in Seattle. Other rocky planets orbiting close to their stars in
tidally-locked orbits could also display such rampant volcanism, Barnes said.

Another study presented at the AAS meeting suggests that the
current form of the planet might not even been its original one: It could be
the core rocky remains of a Saturn-sized gas giant.

Remnant core

The hot dayside temperatures of the planet not only mean
that it could have a vaporized rock atmosphere, but that that atmosphere could
be boiling off of the planet altogether. The rate of solar heating on the
planet could have already cooked off several Earth masses of material from the
planet.

Jackson, of NASA?s Goddard Space Flight Center, modeled the
planet's mass loss and changes in its orbit and effectively turned back the
clock. Jackson and his team found that CoRoT-7b could have once weighed in at
100 Earth masses ? about the mass of Saturn ? when it first formed. At this
point it may have been 50 percent farther from its star than it is now.

The research also showed that regardless of whether the
planet started life as a gas giant or a bigger rocky world, it has probably
lost several Earth masses of material since it first formed.

"You could say that, one way or the other, this planet
is disappearing before our eyes," Jackson said.

Jackson and his team think that other exoplanets close to
their sun could also be evaporating. So-called hot Jupiters ? gas giants whose
orbits hug their star ? could also be undergoing mass loss right now,
eventually leaving behind rocky cores like CoRoT-7b.

And Super-Ios and remnant cores are not mutually exclusive,
Jackson and Barnes said ? CoRoT-7b, and other exoplanets ? could belong to both
classes.